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Now I could be wrong and happy to be proved that way, but EF-S is for a crop sensor body and will have 18mm at 18mm not an EFOV of above as answered.

If this was a EF lens on said body, then the 18mm would have an EFOV of 28.8mm, but it would still be an 18mm lens, so the angle is restricted to an EFOV via the diffenert surface field of the opening of the lens, Correct?

Here is what Canon writes on it's site regarding this lens,

"The EF-S 18-200mm f/3.5-5.6 IS is a compact, EF-S lens with high magnification – approx. 11x. It features an 18-200mm zoom ratio (the 35mm film equivalent focal length is 29-320mm) and has a maximum aperture of f/3.5-5.6. Designed to appeal to entry-level and advanced amateur users looking for a lens with an optical Image Stabilizer and large focal length range, it weighs just 595g and measures 78.6 x 102mm. The lens offers 0.45m minimum focusing distance at all zoom position.

The EF-S 18-200mm f/3.5-5.6 IS is designed exclusively for use with EOS cameras featuring an EF-S lens mount – including the EOS 50D, EOS 1000D, EOS 450D, and earlier models."

So is the author missing the word "FILM" or Full Sized Sensor in his answer? does it sort of make for some confusion when deciding, would for me, and lastly, how is the EFOV to be compaired mentaly when looking at this?

All seems a little bit over the shop to me. The poor bloke asking the question is in his lime light years and speaks of having little to no experience with DSLR, beside a short stint with a Canon Powershot S2 IS.

Now I could be wrong and happy to be proved that way, but EF-S is for a crop sensor body and will have 18mm at 18mm not an EFOV of above as answered.

A focal length is a physical property of a lens.

The field of view provided by that lens in 35mm (aka 135-format) nomenclature is 1.6x the marked focal length (whether it be an EF-S lens with a 'shorter' marked focal length, or an EF lens designed for full-frame cameras, with whatever focal length it specifies.

EFOV = equivalent field of view.

Originally Posted by Roosta

If this was a EF lens on said body, then the 18mm would have an EFOV of 28.8mm, but it would still be an 18mm lens, so the angle is restricted to an EFOV via the diffenert surface field of the opening of the lens, Correct?

An 18mm lens is an 18mm lens, whether it's EF or EF-S.

The '-S' in EF-S designates 'short back-focus', meaning that the lens's rear element protrudes further into the chamber, and is thus closer to the sensor.

Canon designed the EF-S system such that the bayonet mount would also accommodate EF lenses (which are themselves designed for 135-format cameras).

The difference with an EF lens is that the sensor cannot 'see' the entire imaging circle, whereas an EF-S lens is designed such that the the imaging circle's diameter is the same size as the diagonal length of the sensor.

Originally Posted by Roosta

So is the author missing the word "FILM" or Full Sized Sensor in his answer? does it sort of make for some confusion when deciding, would for me, and lastly, how is the EFOV to be compaired mentaly when looking at this?

Greco is correct. What he means is that an 18mm EF-S lens on an APS-C DSLR camera will provide the equivalent framing of a 28mm lens on a 35mm camera (or 'full-frame' DSLR).

As to whether or not Grego's explanation was helpful to the person whose query he answered, I cannot say.

What I can say is that I understand this stuff, but it can be confusing to those who don't.

It makes less sense to people who don't know what kind of framing various lenses provide on a 35mm camera; it's another language, and dare I say it, for the beginners, no matter what format of camera they have, most of them just want to know how much 'stuff' is in the scene at the wide end of a lens, and how much it 'zooms' (ie, its magnification factor).

The field of view provided by that lens in 35mm (aka 135-format) nomenclature is 1.6x the marked focal length (whether it be an EF-S lens with a 'shorter' marked focal length, or an EF lens designed for full-frame cameras, with whatever focal length it specifies.

EFOV = equivalent field of view.

An 18mm lens is an 18mm lens, whether it's EF or EF-S.

The '-S' in EF-S designates 'short back-focus', meaning that the lens's rear element protrudes further into the chamber, and is thus closer to the sensor.

Canon designed the EF-S system such that the bayonet mount would also accommodate EF lenses (which are themselves designed for 135-format cameras).

The difference with an EF lens is that the sensor cannot 'see' the entire imaging circle, whereas an EF-S lens is designed such that the the imaging circle's diameter is the same size as the diagonal length of the sensor.

Greco is correct. What he means is that an 18mm EF-S lens on an APS-C DSLR camera will provide the equivalent framing of a 28mm lens on a 35mm camera (or 'full-frame' DSLR).

As to whether or not Grego's explanation was helpful to the person whose query he answered, I cannot say.

What I can say is that I understand this stuff, but it can be confusing to those who don't.

It makes less sense to people who don't know what kind of framing various lenses provide on a 35mm camera; it's another language, and dare I say it, for the beginners, no matter what format of camera they have, most of them just want to know how much 'stuff' is in the scene at the wide end of a lens, and how much it 'zooms' (ie, its magnification factor).

The age of entitlement isn't over, it's just over there where you can't get to it.
When several possibilities exist, the simplest solution is the best.
"There are no rules" Bruce Barnbaum, The art of PhotographyGraham

Something I find interesting is that the field of view provided by lenses designed for DSLRs with APS-C-sized sensors is almost always expressed in 135-format terms (eg, 18-200mm providing equivalent framing to 28-320mm on a 35mm camera).

It's not an outlandish suggestion that a lot of people new to (D)SLR photography have not necessarily come from the 35mm film world, and that their first cameras were probably point-and-shoot models which have an even smaller sensor; so effectively, describing 35mm-equivalent framing to such a person is like translating French into German when the person just needs plain English.

The 35mm format comparison is useful, however, for those who do know 35mm SLRs and what the focal lengths represent in terms of field of view, and who have moved to a digital SLR with a sensor smaller than the size of a 35mm frame they've used for 30 years.

So when they talk about EFOV - Effective Field Of View, I was of the understanding that it's all relivant to the sensor area, and the FOV is what changes, not so much the focal lenght, which to me, is the way the explanation has been put across.

Am I getting it right ?

P.S. Nice article David, Have loved your work since I came across it on this site. So sound and well written information there to get people out and trying it, I'm sure.

So when they talk about EFOV - Effective Field Of View, I was of the understanding that it's all relivant to the sensor area, and the FOV is what changes, not so much the focal lenght, which to me, is the way the explanation has been put across.

Am I getting it right ?

Bingo.

The size of the sensor does not, and cannot, alter the focal length of the lens, as the focal length is a physical attribute.

The focal length is the distance between the focal plane (ie, sensor or film) and the optical centre of the lens.

The easiest way to illustrate the effect of a 'full-frame' lens when used on a camera with a smaller sensor is as follows:

Go and look outside at a house across the road.

Stay where you are, and then look at the same house through a toilet paper roll.

The toilet paper roll (acting as an EF-S lens in this example) does not change the distance between yourself and the house; nor does it magnify the size of the house.

What the toilet paper roll does achieve is making the house appear larger relative to the size of the frame, which is actually confined by the toilet paper roll.

An EF lens has an imaging circle larger than the size of an APS-C sensor, so while the lens can 'see' what it was designed to see, only a portion of that imaging circle can be projected onto the smaller sensor; the sensor is effectively what does the cropping.

In my example, it's the toilet paper roll (lens) which reduces what you see, whereas when using a real lens and real camera, the EF lens can 'see' more content than can be projected onto the sensor.

None of this, however, has any bearing on the focal length of the lens.

Originally Posted by Roosta

P.S. Nice article David, Have loved your work since I came across it on this site. So sound and well written information there to get people out and trying it, I'm sure.

Re defaulting to "FF" and "crop sensor" comparison to always describe and or explain:

Originally Posted by Xenedis

Something I find interesting is that the field of view provided by lenses designed for DSLRs with APS-C-sized sensors is almost always expressed in 135-format terms (eg, 18-200mm providing equivalent framing to 28-320mm on a 35mm camera).

It's not an outlandish suggestion that a lot of people new to (D)SLR photography have not necessarily come from the 35mm film world, and that their first cameras were probably point-and-shoot models which have an even smaller sensor; so effectively, describing 35mm-equivalent framing to such a person is like translating French into German when the person just needs plain English.

The 35mm format comparison is useful, however, for those who do know 35mm SLRs and what the focal lengths represent in terms of field of view, and who have moved to a digital SLR with a sensor smaller than the size of a 35mm frame they've used for 30 years.

Hear; hear!

****

The two dimensional diagram representation, is similar to the image representation I use.
The images also show the “missing bits” on the sides as well as the top and bottom of the tree.
Below FYI a 50mm lens on two different cameras shooting at the same distance and at the same camera angle and camera elevation.

The 50mm lens on the 5DMkII in the digital darkroom showing the FoV relevance of the smaller sensor (APS-C) camera

Wow William using the images certainly made this topic easier to understand. When I bought my first EF-S 18-55mm lens I was told the S meant you couldn't use it on a film camera body as opposed to a Digital camera body. I was also told the wider end of the lens was equivalent to 28.8mm on a 35mm film camera.

When I bought my first EF-S 18-55mm lens I was told the S meant you couldn't use it on a film camera body as opposed to a Digital camera body. I was also told the wider end of the lens was equivalent to 28.8mm on a 35mm film camera. All quite confusing to me.

Specifically - adding to the technical information:

The “EF-S” and “EF” define the lens mounts (both are bayonet mounts, but are different bayonet mounts).
It is correct to state that an EF-S lens will NOT mate to an “EF” mount Canon film camera, as all canon film cameras (in the EOS range) are “EF” mount, only.

But it is INCORRECT to say, (or imply) that EF-S lenses will mount on (all) “digital” cameras: because only SOME of the Canon digital cameras are EF-S mount.
Specifically, (at time of writing) the Canon Cameras which accept an EF-S mount lens are:

ALL canon APS-C sensor size Cameras conforming to -
 After and including the 20D in that lineage
 After and including the 300D in that lineage
 After and including the 1000D in that lineage
 The 7D
For example:
An EF-S Lens will NOT MOUNT (i.e. will not be able to connect), to a 5D and that is a “digital camera”.
Nor will an EF-S lens mount to any 1D Series camera and they are Digital “Crop Cameras”
Nor will an EF-S lens mount to a 10D and that is a Digital APS-C sensor “Crop Camera”.

The Canon CAMERAS, LENSES and ACCESSORIES (e.g. extension tubes), which are EF-S mount, have a WHITE SQUARE alignment mark, to indicate the EF-S Mount, compatibility.
Some, other brand accessories, with EF-S mount, also sport the White Square alignment mark.

HERE:

***

Also, another area of misinformation is where other (third party) lenses, which designed for APS-C sensors, (i.e. throw an image circle for an APS-C sensor) are described as “EF-S lenses” – they are not.
For example the Tamron 17 to 50F/2.8 is an “EF” lens.

***

A good way to think of Focal Lengths is – your camera (JudiN):

18mm is a bit wide angle and 55mm is a bit telephoto.
If you want really wide sweeping vista landscapes in one shot, then you look at a 10 to 22 type zoom lens.
If you want to get closer at the football then you look at a 70 to 200 type lens . . .
IMO the numbers need to relate to “things I want to photograph”.
For a general guide, it is easier to relate visually to “what can I do with the lens”, I think.

An EF-S Lens will NOT MOUNT (i.e. will not be able to connect), to a 5D and that is a “digital camera”.
Nor will an EF-S lens mount to any 1D Series camera and they are Digital “Crop Cameras”
Nor will an EF-S lens mount to a 10D and that is a Digital APS-C sensor “Crop Camera”.

WW

William, I must disagree, you can mount an EF-S len to a Body designed for EF lens mount only.

It's an aussie invention called "100 Mile an hour Tape"

Some of the advantages of this sytem are, but not limited to,

1, You have the ability to actually move the lens at all sorts of angles,
2, You can basicaly attach any lens you want
3, Not brand or mount specific, for example, if you where unfortunate enough to have, say, "Nikon" lenses, they can easily be mounted to the much more superior "Canon" body
4, No need to take multipul shots to stich for a pano, simply set a longer exposure and move your attached lens on the horizontal plane.

for example, if you where unfortunate enough to have, say, "Nikon" lenses,

Seeing as I have never really understood how people can be so handicapped by using a system ( Canon ) where the same brand lenses and bodies can be incompatible I thought I would point out the vast superiority of the Nikon way of life.
If I were to go out with a "crop" body and a "full frame" body and a bag full of lenses as I frequently do, I know that I can not only physically mount any lens in the bag on either body and at the same time be confident that it will do the job as the maker intended.
As an example, I simply grabbed a "crop" lens this morning and mounted it on a "full frame" body and took a quick snap of the back yard as an example.

The first is straight from the camera ( not set in DX crop mode ) and the second has vignetting control applied in software.

Possibly explains why so many Canon owners buy one of those inferior Nikkor 14-24 lenses and an adaptor to use on their superior cheap bodies.

Andrew

Nikon, Fuji, Nikkor, Sigma, Tamron, Tokina and too many other bits and pieces to list.

I agree with Xenedis' comment that it is silly these days to treat the 44mm diagonal sensor as standard when it relates to the 35mm negative's diagonal. Cameras using that image diagonal are an extreme minority these days so, to the newcomer, it is a bizarre baseline.

I like to think of lens focal lengths in terms of multiples of image diagonal, where: